Field of the Invention
The invention relates to a reversing or turning device for a sheet-fed rotary printing press, having a sheet transport device for accepting a sheet, that has been printed on one side thereof, at a leading edge thereof from an upline sheet-guiding cylinder, reversing the sheet by turning it about a longitudinal axis thereof in a sheet transport direction, and then transferring the sheet, in the reversed condition thereof with a leading edge thereof leading, to a downline sheet-guiding cylinder, and having a cam path extending substantially like that of a Mobius strip for guiding the sheet transport device.
Reversing devices for sheet-fed rotary printing presses have become known heretofore in the prior art and are used in recto/verso or first-form and perfector printing to reverse or turn over a sheet that has been printed on one side thereof, i.e., recto or first form, in upstream printing units so that it can be fed to one or more downline printing units for printing on the nonprinted side thereof. The reversing devices generally known heretofore from the prior art have a storage drum for this purpose, to which the sheets which have been printed on one side thereof are transferred from the impression cylinder of an upline printing unit and temporarily stored and are then taken over at a trailing edge thereof, counter to the direction of rotation of the storage drum, by a gripper device of a downline cylinder. The reversing devices in the prior art have a disadvantage in that the sheet is drawn off by the gripper devices of the downline sheet-guiding cylinder in a direction opposite to a natural direction of motion thereof from the storage drum. Particularly at high printing-press speeds, this change in the direction of motion of the sheet and the attendant change in impetus results in strong forces, which make it more difficult to feed the inverted sheet with maintained registration to the downstream printing units, and has a deleterious effect upon the print quality.
From the published German Patent Document DE-PS 34 44 848 C2 of the applicant of the instant application, a sheet reversing device for sheet-fed rotary printing presses has become known, moreover, wherein the sheet on being transported from an upline printing unit to a downline printing unit is reversed or inverted 180.degree. about the longitudinal axis thereof. The reversal is performed thereat by a chain system with gripper devices secured thereto which extends, in a twisted manner, somewhat like a Mobius strip, between the printing units. Due to the chain system that is used, which is known also to be installed in delivery systems of sheet-fed rotary printing presses, reversal of the sheets while maintaining proper registration is achievable, particularly at high printing speeds, only at considerable technological effort and expense. The system, furthermore, is subject to the disadvantage that the spacing between two gripper bars is predetermined in advance and cannot be varied, the length of the system consequently having to be adapted exactly to the diameter relationships of the printing press.